Rotor for a hover-capable aircraft and related method of control

Abstract

A rotor for a hover-capable aircraft includes a hub rotatable about a first axis and at least two blades hinged to the hub. Each blade has a main portion hinged to the hub and a tip portion, which is arranged radially outermost with respect to first axis with respect to the corresponding main portion. The tip portion of each blade is movable with respect to the corresponding main portion of that blade. The tip portion of each blade is selectively movable with respect to the corresponding main portion of that blade between a first position, in which it defines a dihedral or anhedral angle with respect to the corresponding main portion; and a second position, in which it defines a positive or negative sweep angle with respect to the corresponding main portion.

The invention claimed is: 
     
       1. A rotor ( 3 ′″,  3 ″″) for a hover-capable aircraft ( 1 ), comprising:
 a hub ( 7 ) rotatable about a first axis (A); and 
 at least two blades ( 6 ′″) hinged to said hub ( 7 ); 
 
       each of said at least two blades ( 6 ′″) comprising a main portion ( 10 ) articulated to said hub ( 7 ) and a tip portion ( 11 ′″,  11 ″″), which is arranged radially outermost from said first axis (A) with respect to the corresponding main portion ( 10 ); 
       said tip portion ( 11 ′″,  11 ″″) of each of said at least two blades ( 6 ′″) being movable with respect to the corresponding said main portion ( 10 ) of said at least two blades ( 6 ′″) between:
 a first angular position, in which said tip portion defines a first dihedral or anhedral angle (α) with respect to the corresponding said main portion ( 10 ); and 
 a second angular position, in which said tip portion defines a second dihedral or anhedral or null angle different from the first dihedral or anhedral angle (α) with respect to the corresponding said main portion ( 10 ); 
 
       said rotor ( 3 ′″,  3 ″″) further comprising connecting means ( 60 ′″,  60 ″″) for movably connecting said tip portion ( 11 ′″,  11 ″″) to said main portion ( 10 );
 characterized in that said connecting means ( 60 ′″,  60 ″″) can be selectively set in a first configuration in which said connecting means ( 60 ′″,  60 ″″): 
 allow the rotation of said tip portion ( 11 ′″,  11 ″″) with respect to said main portion ( 10 ) in a first angular direction and up to said first angular position of said tip portion ( 11 ′″,  11 ″″) with respect to said main portion ( 10 ), by means of resultant moments (Mr) generated by inertia forces and aerodynamic forces on said tip portion ( 11 ′″,  11 ″″); and 
 prevent said tip portion ( 11 ′″,  11 ″″) from rotating in a second angular direction, opposite to said first angular direction, with respect to said main portion ( 10 ). 
 
     
     
       2. The rotor of  claim 1 , wherein said connecting means ( 60 ′″,  60 ″″) can be selectively set in a second configuration, in which said connecting means ( 60 ′″,  60 ″″):
 allow the rotation of said tip portion ( 11 ′″,  11 ″″) with respect to said main portion ( 10 ) in said second angular direction and up to said second angular position of said tip portion ( 10 ); and 
 prevent said tip portion ( 11 ′″,  11 ″″) from rotating with respect to said main portion ( 10 ) in said first angular direction. 
 
     
     
       3. The rotor of  claim 2 , further comprising:
 a control unit ( 66 ′″); and 
 an actuator ( 65 ′″), which is controllable by said control unit ( 66 ′″) and is actuatable to set said connecting means ( 60 ′″,  60 ″″) in either said first configuration or said second configuration. 
 
     
     
       4. The rotor of  claim 3 , wherein said actuator ( 65 ′″) is controllable to set said connecting means ( 60 ′″,  60 ″″) in said first configuration, when said hover-capable aircraft ( 1 ) requires to be operated, in use, in hovering;
 said actuator ( 65 ′″) being controllable to set said connecting means ( 60 ′″,  60 ″″) in said second configuration when said hover-capable aircraft ( 1 ) requires to be operated, in forward flight. 
 
     
     
       5. The rotor of  claim 3 , wherein said tip portion ( 11 ′″,  11 ″″) defines the first anhedral angle (α) with respect to the corresponding said main portion ( 10 ) when set, in use, in said first angular position and/or said null angle with respect to the corresponding said main portion ( 10 ) when set, in use, in said second angular position. 
     
     
       6. The rotor of  claim 5 , wherein said actuator ( 65 ′″) comprises an output member ( 73 ′″), which is slidable back and forth parallel to a second axis (F). 
     
     
       7. The rotor of  claim 2 , wherein said connecting means ( 60 ′″,  60 ″″) comprise a hinge ( 61 ′″), which is configured to allow the rotation of said tip portion ( 11 ′″,  11 ″″) with respect to said main portion ( 10 ) about a second axis (F). 
     
     
       8. The rotor of  claim 7 , wherein said connecting means ( 60 ′″,  60 ″″) comprise:
 at least one first coupling element ( 80 ′″,  80 ″″) carried by one ( 11 ′″,  11 ″″) of said tip portion ( 11 ′″,  11 ″″) and said main portion ( 10 ); and 
 at least one second coupling element ( 81   a ′″,  81   b ′″;  81   a ″″,  81   b ″″) carried by the other ( 11 ′″,  11 ″) of said tip portion ( 11 ′″,  11 ″″) and said main portion ( 10 ); 
 said at least one first and at least one second coupling elements ( 80 ′″,  80 ″″;  81   a ′″,  81   b ′″;  81   a ″″,  81   b ″″) being selectively movable with respect to one another and parallel to said second axis (F) between a first axial position in which said at least one first and at least one second coupling elements ( 80 ′″,  80 ″″;  81   a ′″,  81   b ′″;  81   a ″″,  81   b ″″) are engaged with one another and a second axial position in which said at least one first and at least one second coupling elements ( 80 ′″,  80 ″″;  81   a ′″,  81   b ′″;  81   a ″″,  81   b ″″) are disengaged. 
 
     
     
       9. The rotor of  claim 8 , wherein said at least one first and at least one second coupling elements ( 80 ′″;  81   a ″″,  81   b ″″) comprise respective first and second disks ( 82   a ′″,  82   b ″″;  86   a ′″,  86   b ″″), which comprise respective plurality of first and second toothed surfaces ( 83   a ′″,  83   b ′″;  87   a ′″;  87   b ′″) meshing with one another, when said at least one first and at least one second coupling elements ( 80 ″″;  81   a ″″,  81   b ″″) are set, in use, in said first axial position;
 said plurality of first and second toothed surfaces ( 87   a ′″,  87   b ′″) being shaped in such a way to allow the rotation of said at least one first and at least one second coupling elements ( 80 ′″,  80 ″″;  81   a ′″,  81   b ′″;  81   a ′″,  81   b ′″) both in said first angular direction and in said second angular direction; 
 said at least one first coupling element ( 80 ′″) comprising at least one one-way free-wheel clutch ( 84 ′″,  85 ′″), which is interposed between said first disk ( 82   a ′″,  82   b ′″;  86   a ′″,  86   b ′″) and said relative one ( 10 ) of said tip portion ( 11 ′″) and said main portion ( 10 ). 
 
     
     
       10. The rotor of  claim 8 , wherein said at least one first and at least one second coupling elements ( 80 ″″;  81   a ″″,  81   b ″″) comprise respective first and second disks ( 82   a ″″,  82   b ″″;  86   a ″″,  86   b ″″), which comprise respective plurality of first and second toothed surfaces ( 83   a ″″,  83   b ″″;  87   a ″″;  87   b ″″) meshing with one another, when said at least one first and at least one second coupling elements ( 80 ″″;  81   a ″″,  81   b ″″) are set, in use, in said first axial position;
 said plurality of first and second toothed surfaces ( 83   a ″″,  83   b ″″;  87   a ″″;  87   b ″″) being shaped in such a way to allow the intermittent rotation of said at least one first and at least one second coupling elements ( 80 ″″;  81   a ″″,  81   b ″″) in a respective one of said first angular direction and second angular direction and to prevent that rotation in respective another of said first direction and second direction. 
 
     
     
       11. The rotor of  claim 10 , wherein first and second teeth of said plurality of first and second toothed surfaces ( 87   a ″″,  87   b ″″) are saw-tooth shaped. 
     
     
       12. The rotor of  claim 10 , wherein said at least one first coupling element ( 80 ″″) comprises, in turn:
 a first splined body ( 95 ″″) movable about said second axis (F); and 
 at least one second splined body ( 96 ″″), which is angularly and axially movable integrally together with said first disk ( 82   a ″″,  82   b ″″); 
 said at least one second splined body ( 96 ″″) being axially movable and angularly integral with respect to said first splined body ( 95 ″″). 
 
     
     
       13. The rotor of  claim 12 , further comprising:
 a control unit ( 66 ′″); and 
 an actuator ( 65 ′″), which is controllable by said control unit ( 66 ′″); 
 wherein said actuator ( 65 ′″) comprises an output member ( 73 ′″), which is slidable back and forth parallel to the second axis (F), and the rotor further includes first elastic means ( 100 ″″,  101 ″″) interposed between said output member ( 73 ″″) and said at least one second splined body ( 96 ″″), and configured to elastically load said at least one second splined body ( 96 ″″) towards said first axial position. 
 
     
     
       14. The rotor of  claim 13 , further comprising second elastic means ( 90 ′″), which are interposed between said main portion ( 10 ) and said tip portion ( 11 ′″,  11 ″″) and are configured to elastically load, in use, said tip portion ( 11 ′″,  11 ″″) towards one of said first or second angular position. 
     
     
       15. The rotor of  claim 8 , further comprising:
 an actuator ( 65 ′″) with an output member ( 73 ′″); 
 wherein said at least one first coupling element ( 80 ″″) is carried by said main portion ( 10 ) and said at least one second coupling element ( 81   a ″″,  81   b ″″) is carried by said tip portion ( 11 ′″,  11 ″″); 
 said at least one first coupling element ( 80 ″″) being movable together with said output member ( 73 ″″) parallel to said second axis (F). 
 
     
     
       16. The rotor of  claim 1 , further comprising damping means ( 91 ′″) which are interposed between said main portion ( 10 ) and said tip portion ( 11 ′″,  11 ″″) and are configured to exert, in use, a damping moment (Md) on said tip portion ( 11 ′″,  11 ″″). 
     
     
       17. The rotor of  claim 1 , wherein said main portion ( 10 ) comprises at least one ballast ( 91 ′″). 
     
     
       18. A method of controlling a rotor ( 3 ′″,  3 ″″) for a hover-capable aircraft ( 1 ); said rotor ( 3 ′″,  3 ″″), comprising:
 a hub ( 7 ) rotatable about a first axis (A); and 
 at least two blades ( 6 ) hinged to said hub ( 7 ); 
 
       each of said at least two blades ( 6 ) comprising a main portion ( 10 ) hinged to said hub ( 7 ) and a tip portion ( 11 ′″,  11 ″″), which is arranged radially outermost with respect to said first axis (A) with respect to the corresponding main portion ( 10 );
 said method comprising the steps of: 
 i) connecting said tip portion ( 11 ′″,  11 ″″) in movable way with respect to said main portion ( 10 ); 
 ii) moving said tip portion ( 11 ′″,  11 ″″) with respect to said main portion ( 10 ) between: 
 a first angular position, in which said tip portion defines a first dihedral or anhedral angle (α) with respect to the corresponding said main portion ( 10 ); and 
 a second angular position, in which said tip portion defines a second dihedral or anhedral angle (α) or a null angle, different from said first dihedral or anhedral angle (α), with respect to the corresponding said main portion ( 10 ); 
 said method being characterized by comprising the steps of selectively: 
 iii) allowing the rotation of said tip portion ( 11 ′″,  11 ″″) with respect to said main portion ( 10 ) in a first angular direction and up to said first angular position, by means of resultant moments (Mr) generated by inertia forces and aerodynamic forces on said tip portion ( 11 ′″,  11 ″″); and 
 iv) preventing said tip portion ( 11 ′″,  11 ″″) from rotating in a second angular direction, opposite to said first angular direction, with respect to said main portion ( 10 ). 
 
     
     
       19. The method of  claim 18 , further comprising the further steps of selectively:
 v) allowing the rotation of said tip portion ( 11 ′″,  11 ″″) with respect to said main portion ( 10 ) in said second angular direction and up to said second angular position of said tip portion ( 11 ′″,  11 ″″); and 
 vi) preventing said tip portion ( 11 ′″,  11 ″″) from rotating with respect to said main portion ( 10 ) in said first angular direction. 
 
     
     
       20. The method of  claim 19 , wherein said step v) is carried out when said hover-capable aircraft ( 1 ) is in forward flight with a speed greater than a threshold value and said hover-capable aircraft ( 1 ) needs to be operated in hover and/or when said hover-capable aircraft ( 1 ) is in hover; and/or said step vi) is carried out when said hover-capable aircraft ( 1 ) is in hover and said hover-capable aircraft ( 1 ) needs to be operated in forward flight. 
     
     
       21. The method of  claim 19 , further comprising the steps of:
 vii) keeping said tip portion ( 10 ′″,  10 ″″) in said first angular position, when said hover-capable aircraft ( 1 ) is in hover and said hover-capable aircraft ( 1 ) needs to be operated in said hover; and/or 
 viii) keeping said tip portion ( 10 ′″,  10 ″″) in said second angular position, when said hover-capable aircraft ( 1 ) is in forward flight and said hover-capable aircraft ( 1 ) needs to be operated in said forward flight. 
 
     
     
       22. The method of  claim 19 , further comprising at least one of the steps ix) of generating an elastic moment (Mk) on said tip portion ( 10 ′″,  10 ″″) and x) of generating a damping moment (Md) on said tip portion ( 10 ′″,  10 ″″);
 a lift acting on said tip portion ( 11 ′″,  11 ″″) generating an aerodynamic moment (Mlift) being directed in said second angular direction when said hover-capable aircraft ( 1 ) is in hover or in forward flight with a speed lower than a threshold value; said aerodynamic moment (Mlift) being directed in said first angular direction when said hover-capable aircraft ( 1 ) is in forward flight with a speed greater than said threshold value and at least for one angular position of said at least two blades ( 6 ′″,  6 ″″) with respect to said first axis (A); 
 wherein one resulting moment (Mr) of said resultant moments (Mr) on said tip portion ( 10 ′″,  10 ″″) being directed in said second angular direction when said hover-capable aircraft ( 1 ) is in hover or in forward flight with a speed lower than said threshold value, and being directed in said first angular direction when said hover-capable aircraft ( 1 ) is in forward flight with a speed greater than said threshold value and at least for said one angular position of said at least two blades ( 6 ′″,  6 ″″) with respect to said first axis (A). 
 
     
     
       23. A hover-capable aircraft, comprising:
 a main rotor ( 3 ,  3 ′,  3 ″) according to  claim 1 ; and 
 a control unit ( 40 ) programmed to arrange said tip portions ( 11 ′″,  11 ″″) of said at least two blades ( 6 ′″) in the respective said first angular positions when said hover-capable aircraft ( 1 ) is in hovering conditions and in the respective said second angular positions when said hover-capable aircraft ( 1 ) is in forward flight conditions.